Natural gas hydrates encase predominantly methane, but also higher hydrocarbons as well as CO2 and H2S. The formation of gas hydrates from a changing gas mixture, either due to the preferred incorporation of certain components into the hydrate phase or an inadequate gas supply, may lead to significant changes in the composition of the resulting hydrate phase. To determine the overall composition of a hydrate phase during the hydrate formation process, Raman spectroscopy is regarded as a non-destructive and powerful tool. This technique enables to distinguish between guest molecules in the free gas or liquid phase, encased into a clathrate cavity or dissolved in an aqueous phase, therefore providing time-resolved information about the guest molecules during the hydrate formation process.
Experiments were carried out at the Micro-Raman Spectroscopy Laboratory, GFZ. Mixed gas hydrates were synthesized in a high-pressure cell from pure water and a specific gas flow containing CH4, C2H6, C3H8, iso-C4H10 and n-C4H10 at 274 K and 2.20 MPa. Three potential different gas supply conditions were selected for the formation of mixed gas hydrates, namely an open system (test scenario 1) with a continuous gas supply, a closed system (test scenario 2) with no gas supply after initial pressurization with the gas mixture, and a semi-closed system (test scenario 3) with only an incoming gas but a disrupted outlet. In situ Raman spectroscopic measurements and microscopic observations were applied to record changes in both gas and hydrate compositions over the whole formation period until it reached a steady state. In all three test scenarios, 12 hydrate crystals were selected and continuously characterized for 5 days with single point Raman measurements to record the formation process of mixed gas hydrates. Each test scenario was repeated for 3 times, therefore resulting in 9 separate experimental tests.
This dataset encompasses raw Raman spectra of the 9 experimental tests (.txt files) which contained Raman shifts and the respective measured intensities. Each Raman spectrum was fitted to Gauss/Lorentz function after an appropriate background correction to estimate the band areas and positions (Raman shift). The Raman band areas were then corrected with wavelength-independent cross-sections factors for each specific component. The concentration of each guest molecule in the hydrate phase / gas phase was given as mol% in separate spreadsheet for three different test scenarios. Further details on the analytical setup, experimental procedures and composition calculation are provided in the following sections.
Extremophiles maintain an active metabolism up to 122 °C (Takai et al. 2008). These extreme conditions are found, for example in hot springs, in deep oceanic and crustal sediments and in hydrothermal vents at mid-oceanic spreading ridges (Edwards et al., 2011; Heuer et al., 2020). Several studies have investigated the diversity of microorganisms and their relationship to the geological environment as well as to responses to changes. However, the physicochemical parameters necessary to sustain metabolism under these conditions, including the stability of essential molecular compounds like adenosine triphosphate (ATP) and adenosine diphosphate (ADP) have been only studied marginally.
Adenosine triphosphate and adenosine diphosphate are essential energy stores in all currently known metabolic systems. In living cells, the energy is released by the enzymatically controlled exergonic hydrolysis of ATP to power other vital endergonic processes. The abiotic hydrolysis of ATP is kinetically enhanced at elevated temperatures and low pH values resulting in a very short lifetime of ATP and ADP in aqueous solutions (Hulett 1970; Khan and Mohan 1974; Leibrock et al. 1995). Therefore, the kinetic stability of ATP plays a crucial role in metabolism at extreme temperatures. This aspect has been proposed as a critical factor in determining the limits of living cells (Bains et al. 2015).
This data publication compromises all Raman spectra obtained for solutions of Na2ATP with an initial pH of 3 and 7 at 80 °C, 100 °C and 120 °C and for solutions of Na2ADP with initial pH 5 at 100 °C and 120 °C. A hydrothermal diamond anvil cell (HDAC) coupled to a Raman spectrometer was used for in-situ measurements. Pressure was estimated from the vapor-liquid curve of water. In addition to the Raman spectra, the following data are provided: an assignment of peaks in the fitted spectral range, the initial fit parameters, and the fit results.
In biochemical systems, enzymes catalyze the endergonic phosphorylation of adenosine diphos-phate (ADP) to adenosine triphosphate (ATP) by different pathways, e.g., oxidative phosphoryla-tion catalyzed by membrane bound ATP synthase or substrate-level phosphorylation. The stored energy is released by the enzymatically controlled exergonic hydrolysis of ATP to power other vital endergonic reactions; therefore, ATP is widely known as the universal energy currency. Rapid abiotic ATP hydrolysis kinetics thus means higher maintenance energy costs for cells, and it has been suggested that this is an important factor in setting the limits to the functioning of living organisms (Bains et al. 2015). In order to evaluate the running conditions of the in-situ procedure by Moeller et al. (2022) using Raman spectroscopy opened up an efficient way of obtaining further insights to the effects of P-T- ionic composition on the kinetics of ATP-ADP hy-drolysis. Raman spectroscopy can be combined with a hydrothermal diamond anvil cell, which provides an isochoric system for measurements up to pressures of 2000 MPa. Another system for in-situ Raman spectroscopy at elevated pressures and temperatures is based on an autoclave fitted with optical high-pressure windows, as shown by Louvel et al. (2015) and works up to 200 MPa. In this system, pressure and temperature can be controlled independently, so that isobaric temperature series are possible.
This data publication compromises all Raman spectra measured in-situ of Na2H2ATP solutions at 80, 100 and 120 °C and up to 1666 MPa to determine the rate constants of the hydrolysis of adenosine triphosphate (ATP) to adenosine diphosphate (ADP) at 48 different P-T conditions. Furthermore, an assignment of peaks in the fitted range, the initial fit parameters and the fit-results are provided. Besides the kinetic data, the pH of the ATP solutions was calculated at experimental temperature and pressure conditions.